Alright, let me see if I get this straight:
Your character is somehow overlapping the door (I suppose there’s some sort of collision box or sphere around the door) which indicated that the player is close enough to interact with the door.
Furthermore, your character picked up the correct key to open that specific door (hence your switch).
Now you’ve created the interface. Did you implement the interface in the door actor? The seconds image you’ve uploaded in your previous comment, is that in the event graph of your door actor?
To clarify my assumptions:
It looks to me like your character (in which you have your IA_Interact event) is correctly set up. Your looping your overlapping actors and calling the interface on all actors, if they implement said interface.
But it also looks like your door actor (the first image in your previous comment) have not yet implemented the interface, but instead has a custom event in the event graph, in which you check whether the correct key have been picked up, and here you also try to call the interface.
The first image of your previous post, is that from an event on your door actor, or it that image also from your character?